Simple mode: Cannot use empty string matching for last group of regex

[Billiam]

I think this is a bug, but might just be a documentation issue.

It seems like simple mode's regex can match an empty string for any group except the last group of the regex.
Otherwise, Uncaught TypeError: Cannot read property 'text' of undefined will be thrown when entering on the next line (see video)

I believe matching an empty string is intended behavior, based on the solution given in #5374

Example: https://codepen.io/billiam/pen/poNxZMw

simplemode.mp4

[marijnh]

That was a bug. Attached patch should fix it.